The presence of food in the mouth activates the parasympathetic nervous system (PNS) and initiates the pre-absorptive release of insulin. To determine the relative effects of neural stimulation of the pancreas and the presence of early insulin on glucose metabolism following a meal, normal weight and obese subjects (n=6 per group) will be admitted into the Clinical Research Center for 4 nights over an 8 day period. Each subject will undergo 4 experimental conditions administered in a counter-balanced order: 1) saline infusion; 2) 10 min infusion of insulin simultaneously with meal ingestion (0.24U bolus: 15 mU/m2/min); 3) atropine infusion (0.4 mg/m2 bolus; 0.4 mg/m2/hr for 4 hrs); 4) insulin and atropine infusion as above.